'Concordancers':
These are some good 'Concordancer(s)' that I've found:
http://quod.lib.umich.edu/cgi/c/corpus/corpus?page=home;c=micase;cc=micase (MICASE: Michigan Corpus of Academic Spoken English)
http://www.lextutor.ca (Compleat Lexical Tutor)
http://www.lextutor.ca (Compleat Lexical Tutor)